Objective: To evaluate, for the first time, the safety and efficacy of long-term ventralis intermedius (Vim) constant current deep brain stimulation (DBS) in essential tremor (ET), and to compare the outcomes to published studies using traditional constant voltage DBS.

Background: Vim DBS is an established intervention for medication-refractory essential tremor. The safety and efficacy of constant current DBS is well documented. Until recently, at King’s College Hospital, constant voltage DBS was used in patients with essential tremor. However in the past few years, the stimulation modality has been changed to a constant current system. No previous reports have carried out a head-to-head comparison between these two modalities of Vim DBS in essential tremor.

Methods: All patients diagnosed with medication-refractory ET and undergone an uninterrupted period of Vim constant current DBS for 3 years were assessed. Clinical outcomes were evaluated using the Fahn–Tolosa–Marin (FTM) tremor rating scale at baseline and postoperatively at the time of evaluation, using the Wilcoxon signed-rank test. Results were compared to results from constant voltage DBS published studies using the unpaired t test with Welch’s correction.

Results: 10 patients (5 men) were assessed, with a median age at evaluation of 74 years (range 66-79) and a mean time of 49.7 (range 36–78) months since initial stimulation. Constant current Vim DBS was well tolerated and effective in all patients with a mean improvement of 65.6% (68 vs 23, p=0.0020) in the total FTM rating scale score. When comparing postoperative mean improvements between constant current and constant voltage modalities, the former group experienced a greater benefit with a significant mean difference of 26% (SEM ± 3%, p< 0.0001) in FTM total score.

Conclusions: Long term constant current Vim DBS is a safe and effective intervention for essential tremor, whose clinical benefits are superior to the standard constant voltage stimulation modality. This could be due to the uniform charge transmitted to the active electrodes regardless of the impedance. Limitations included a small sample size and the variability of impedance in each patient.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/clinical-outcome-of-constant-current-deep-brain-stimulation-in-patients-with-medication-refractory-essential-tremor/